1. Field of the Invention
The invention is new compositions, delivery systems, and methods suitable for the enhanced oil recovery process.
2. Description of the Related Art
Surfactants are used in the enhanced oil recovery process. The presence of surfactant at water and oil interface facilitates oil recovery. It would be ideal to have a sustained and constant concentration at the interface.
Surfactants and other chemicals are often mixed with water and driven into the reservoir in the enhanced oil recovery (EOR) process. Surfactant molecules, especially anionic surfactants, adsorb to the rock before they interact with oil. Adsorption of the surfactant results in the loss of effective amount of surfactant for mobilizing the oil. The adsorption problem worsens when anionic surfactants encounter carbonate rocks that are Lewis acid in nature.
In addition to adsorption, some surfactants precipitate with cations from the rock and from the saline water. In either case, some surfactants are lost before they have a chance to solubilize oil. The exact amount of surfactant adsorption depends on the type of rock, pore surface area, water salinity and the type of surfactants. In general, roughly one milligram of surfactant may adsorb to one gram of rock.
Conventional methods feed surfactant solution into the reservoir directly. The active surfactant gets consumed readily at the oil-water interface. The approach fails to maintain a constant concentration over an extended period of time.
Moreover, conventional methods feed surfactant solution into the reservoir directly. Significant amount of surfactant is lost due to adsorption to the rock, before it has a chance to see residual oil.
To overcome these problems, one may increase the loading of surfactants in water, allowing extra surfactants to be absorbed by the rock, and delivering the remaining surfactants to the oil/water interface. However, additional surfactant cost impacts negatively on the viability of such a process. Alternatively, other researchers tried to use sacrificial chemicals to passivate the rock surface such that surfactant adsorption is mitigated.